TextExpander

Let’s say it’s your job to remind people to do something. Maybe you are the accounts receivable person, and you regularly need to remind people to pay you in 15 days. If you use TextExpander, your days of looking at the calendar and calculating that date are over!
We added date and time math capability to TextExpander 2.5 and above!
In this example, you can create a snippet that automatically inserts a date that is 15 days from today.
Here’s how:
1) Create a new snippet by clicking on the plus (+) sign under your list of snippets on the left in the TextExpander Preference pane.
Dates - Add Days

2) Click on the plus (+) sign under the snippet content pane on the right. Choose Date/Time Math > Add Day(s).
TextExpander

3) TextExpander inserts %@+1D into your snippet content pane. Change “1D” to “15D”.
Dates - Add a month

4) Insert the date format you wish to appear, again using the plus (+) sign menu on the right. For example, if you want the date to appear in formatted “October 29, 2012, insert the following: - Choose Date > Month > January. Add a space.
Dates - Add a day

- Choose Date > Day > 1. Add a comma and space.
Dates - Add a year

- Choose Date > Year > 2001
TextExpander - How it should look

5) When you are done, the snippet content should be: %@+15D%B %e, %Y
TextExpander - Add your label and abbreviation

Give your snippet an abbreviation, such as “d15″ or “payupnow”.